Atrial fibrillation (AF) is the most common arrhythmia and affects about 3 million Americans, a number that is expected to rise to between 6 and 12 million by 2050. AF is a major public health burden as it is associated with a five-fold increased stroke risk, doubling in dementia risk, tripling in heart failure risk and nearly two-fold increasein mortality. Furthermore, the estimated excess cost of AF in the US is nearly $26 billion annually. Despite the profound socioeconomic costs of AF, our understanding of the fundamental mechanisms for the arrhythmia remains limited. Studies have consistently demonstrated that AF, and particularly early onset AF, is heritable. In recent years, we have led the international AFGen Consortium consisting of investigators from over 30 studies. We have identified multiple genetic loci through genome-wide association studies. We now propose a resource efficient program to conduct analyses of extant exome chip and exome sequencing data from AFGen cohorts. We will conduct bioinformatics-informed replication for genomic variant discovery in independent AF cases and controls followed by functional evaluation of the top genes. Our specific aims are: Aim 1. To discover AF-associated variants using extant exome chip data from 21 studies. Aim 2. To discover AF-associated variants in extant exome sequencing data from 7 studies. Aim 3. To replicate AF variants and genes identified in exome chip and exome sequencing projects by: A) Replicating the top 400 SNPs in 5,366 independent AF cases and 9,792 referents without AF; B) Replicating the top 10 genes associated with AF by candidate gene screening in 3,000 individuals with AF and 3,000 individuals without AF. Aim 4.To characterize the electrophysiological phenotype of the top 25 newly identified AF genes in stem cell-derived cardiomyocytes, a zebrafish model system, and by cellular electrophysiology. We have developed innovative techniques for serial assessment of gene knockout or overexpression in induced pluripotent stem cell-derived cardiomyocytes. We will also examine the cardiac effects of gene knockdown or overexpression in zebrafish, followed by analyses of the atrial action potential duration, heart rate, and contractile function. Finally, if the AF varant resides in an ion channel, we will study the variant using patch clamp electrophysiology. We bring together a highly productive, multi-disciplinary, international consortium of AF investigator with expertise in AF epidemiology, AF genetics, bioinformatics, statistical genetics, developmental biology, and cellular electrophysiology. We anticipate that our translational approach will facilitate a greater understanding of the molecular basis of this common and morbid arrhythmia. Identification of causative variants may enhance risk stratification, and will provide preventive and therapeutic targets for drug discovery in the broader scientific and pharmaceutical community.